In recent years, a compact and efficient motor has been sought as a motor for driving an electric vehicle, a hybrid vehicle and others. Research has thus been conducted on various motors such as a synchronous reluctance motor and an embedded magnet synchronous motor.
Among these, Japanese Patent Laying-Open No. 10-150754 discloses an example of the reluctance motor, in which a slit provided at a rotor portion of a flux-barrier motor is designed to vary in width to improve efficiency. In particular, the patent document discloses in FIG. 7 that a slit is formed to have a width smaller at a leading position ahead of the magnetic pole center than at a trailing position, with respect to a rotation direction.
When a motor is used for driving an electric vehicle, a hybrid vehicle and others, an important characteristic of the motor is that it performs regenerative operation. In the conventional method of improving performance, performance during power running has mainly been pursued, while performance during regenerative operation has hardly been pursued.
As to the motor vehicle in particular, a battery is mounted thereon to serve as a direct current power supply for driving a motor, and hence its voltage fluctuations during power running and regenerative operation are not negligible. It is therefore required to improve performance in a well-balanced manner between power running and regenerative operation in consideration of the voltage fluctuations.